What Does Air Pollution Do to Rocks and Metal?

Types of Air Pollutants

• The way air pollution affects a rock or a metal will depend on the kind of pollutant the rock or metal faces. Among pollutants found in the atmosphere are gaseous molecules like sulfur dioxide and carbon monoxide; solid matter ranging from large particulates like dust to small, fine ones like nitrates; and toxic materials like asbestos fibers and lead. (See Reference 1, Reference 2) Though toxic materials are detrimental to human well-being, gases and particulates are especially damaging to metals and rocks.

Effects of Air Pollution on Rocks

• Whether a feature of the natural landscape or a structural component of a building, a rock stands at risk of erosion. Acid rain, formed when gaseous pollutants combine with atmospheric water, weakens rock, allowing water and particulate matter to erode its surface. (See Reference 3, Reference 4) Sedimentary rocks are strongly susceptible not only to erosion but also to chemical reactions with gaseous pollutants that change its composition. Sulfur dioxide combines with compounds in limestone to make gypsum, which settles over limestone as a crust. (See Reference 3)

Effects of Air Pollution on Metals

• Like rock, metal can be worn away by particulates and acid rain. Metals also react chemically with compounds in the atmosphere, resulting in corrosion, or rust, often more noticeable than crust formed on rocks. Corrosion occurs when chemical reactions degrade a metal. Some metals, like iron, corrode simply in the presence of oxygen and water. In other cases; however, such air pollutants as sulfur dioxides and chlorides facilitate the reaction between metal and air, causing the corrosion.

Responses to Air Pollution's Effects on Rocks and Metals

• In some cases of corrosion, rust can be removed from a metal's surface by exposing it to other compounds that decompose it. Erosion proves more difficult to combat, as it wears away original material, whether metal or rock, for good. Because human activities like fossil fuel consumption and pesticide application contribute to air pollution along with natural events like volcanic eruptions, researchers continue to emphasize the effects these activities have on the planet, including its rocks and metals.